Development of a coupled neutronics and thermal hydraulics code with an advanced spatial mapping model

Multi-physics coupling schemes between 3D transport and sub-channel thermal hydraulic are needed to improve the design methodologies and the prediction of local safety margins for both LWR and innovative reactors. In this paper, the coupling of a sub-channel analysis code COBRA-IIIC/MIT2 and an in-house developed neutronics code MOCHA_–2D1D has been developed and a spatial mapping model based on the function-fitting method has been embedded in the coupling scheme. To validate the coupled code, a PWR 3x3 mini assembly problem was tested and compared with a coupled code MCNP5/SUBCHANFLOW developed by KIT. Meanwhile the prediction of the pins power of a Qinshan Phase I NPP 15x15 PWR fuel assembly problem was carried out. All the simulations were found to have converged for an acceptable number. The comparison of the results shows a good agreement and the prediction of the power distribution as expected. The relaxation parameter has been discussed in this paper and an appropriate value has been selected. Further application of the coupled code will be carried out on the HPC for full core simulation and the transient coupled scheme will be developed in next stage. (author)